Apparatus for uniformly distributing a disintegrated fibrous material on a fibre layer forming surface

ABSTRACT

An apparatus for uniformly distributing a disintegrated material on a fiber layer forming surface comprising a cylindrical housing having a perforated plane-surfaced bottom wall, an inlet opening for a stream of air containing suspended fibers and a stirrer having impellers rotating a short distance above the perforated bottom wall.

United States Patent [72] lnventor Torben Borup Rasmussen Tousvej. Denmark [21] Appl. No. 775,479 [22] Filed Nov. 13, 1969 [45] Patented June 1, 1971 [73] Assignee Kark Kristian Kobs Kroyer Aarhus-Vibg, Denmark [32] Priority Nov. 15, 1967 [33] Denmark [31 5702 [54] APPARATUS FOR UNIFORMLY DISTRIBUTING A DISINTEGRATED FIBROUS MATERIAL ON A FIBRE LAYER FORMING SURFACE [50] Field of Search 118/308, 312; 222/l89,238;239/40, 102

[56] I References Cited UNITED STATES PATENTS l,864,740 6/l932 Knapp et al 222/189 2,949,312 8/1960 Anderson 222/189 Primary Examiner-John P. McIntosh Attorney-Watson, Cole, Grindle & Watson ABSTRACT: An apparatus for uniformly distributing a disintegrated material on a fiber layer forming surface comprising a 3 Claims 2 Drawmg cylindrical housing having a perforated plane-surfaced bottom [52] U.S. Cl 118/312, wall; an inlet opening for a stream of air containing suspended 222/238 fibers and a stirrer having impellers rotating a short distance [51 Int. Cl t. B055 7/14 above the perforated bottom wall.

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INVENI OR Mani," 4% 1M ATTORNEY APPARATUS FOR UNIFORMLY DISTRIBUTING A DISINTEGRATED FIBROLS MATERIAL ON A FIBRE LAYER FORMING SURFACE BACKGROUND OF THE INVENTION This invention relates to an apparatus for uniformly distributing a disintegrated fibrous material on a fiber layer forming surface and in particular to an apparatus for the production of a uniform fiber layer on a moving foraminous screen.

In the past fibrous materials such as cellulose pulp have been disintegrated in a hammer mill and a stream of gas originating from said hammer mill and containing suspended fibers has been passed through pipes to a shaft mounted above a fonning screen. The air carrying said fibers to the shaft has been passed through said forming screen by means of a suction box located below said screen so as to form a fiber layer on said screen.

However, the individualized suspended fibers formed in said hammer mill and especially short vegetable fibers tend to entangle and clot as they encounter each other in air suspension during the passage through said pipes. Furthermore, if a high fiber concentration in the air is used in order to secure a high rate of production a further tendency to flocking is induced. Also the impinging of the suspended fibers on pipe walls for both straight runs and turns enhances the clotting. Thus, instead of individual fibers, clots or lumps of fibers are deposited on the fiber layer forming surface and a nonuniform product is formed. In an attempt to avoid said clotting or lump formation during the transportation of the fibers from the hammer mill to the fiber layer forming surface the hammer mill has been located a short distance above the fiber layer forming screen. However, in this case the flow of air generated by the hammers of said hammer mill will interfere with the regularity of the fiber layer deposited on the fiber layer forming screen.

The object of the invention is to avoid fiber clots or lumps in the fiber layer formed on the fiber layer forming surface and to obtain a uniform fiber layer.

SUMMARY OF THE INVENTION The present invention provides an apparatus comprising a housing having a perforated bottom wall, inlet means for a stream of gas containing suspended fibers and a stirring device having impellers mounted for rotation a short distance above the upper surface of said perforated bottom wall. In the apparatus of the invention fiber clots or lumps carried into the housing through said inlet means, or clots or lumps formed in said housing, are subjected to a grinding treatment between the perforated bottom wall and the rotating impellers. This treatment causes said lumps or clots to dissolve and causes the size of such portions of the fibrous material which have not been sufiiciently disintegrated in the hammer mill to be reduced. By suitably adjusting the size of the holes and the total free area of said perforated bottom wall as well as the distance between the impellers and the perforated bottom wall the fineness of the product passing through the bottom wall may be controlled to regulate the production rate.

In a preferred embodiment of the invention the stirring device comprises a central shaft supporting at least two auxiliary shafts, each having at its upper end a friction wheel engaging an annular ring connected to the top of the housing and at its lower end a set of impellers.

By using such a stirring device there is obtained a very uniform distribution of the fibers across the fiber layer forming surface. This construction also allows the use of a single motor for driving the two sets of impellers.

The perforated bottom wall is preferably in the form of a screen.

In some cases fibrous lumps-so-called fish-eyes may be formed in the apparatus of the invention. Such lumps may be built up around pieces of material not having been completely disintegrated prior to being introduced into the housing or formed in the housing itself of coherent individual fibers.

If the stirring device cannot disintegrate these lumps completely a gradual accumulation of them may take place in the housing. These fibrous lumps will gradually make it impossible to obtain the desired uniform distribution of the fibers across the fiber layer forming surface and cause that the apparatus has to be stopped at intervals for removal of the fibrous lumps.

in orderto overcome this difficulty the apparatus may be provided with a narrow slit in the sidewall of the housing close to the screen and an air nozzle may be placed at said slit, said air nozzle being connected to a source of compressed air and being located so as to allow an air current produced therein to pass out through the slit.

The fibrous lumps which are introduced into, or are formed on, the screen will move along the same when being exposed to the effect of the stirring device. When moving along the screen they will at one time pass the slit where they will be exposed to the influence of the air current from the air nozzle placed at this slit. Consequently, they are blown out of said housing.

As the area, in which the said air current is active, is limited, this air current will have no adverse effect on the fiber movement through the screen or on the other fibers in the housing.

By using an adjustable height of the slit a greater or smaller part of the lumps on the screen can be removed from the housmg. K

In a preferred embodiment of the apparatus the slit is connected with a device for the disintegration of the fibrous lumps by means of a pipe, and the apparatus may also have a pipe for recycling the fibers to the housing.

When using this apparatus the fibrous lumps are subjected to a disintegration immediately upon removal from the screen and the disintegrated material formed can, if desired, be recirculated to the distributor.

The device for the disintegration of lumps suitably consists of a container provided with one or more air nozzles connected to a source of compressed air. By means of the air current or currents produced by the nozzles the fibrous lumps can be subjected to a powerful circulating and screw-shaped motion whereby lumps are divided into individual fibers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in vertical section through an apparatus according to the invention and 7 FIG. 2 is a horizontal view along the line II-II in the apparatus shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings 1 is a distributor consisting of a cylindrical top 2 and a detachable lower part 3, the bottom of which is in the form of a screen 4. The distributor l is placed above a gas permeable forming surface 5, such as a web which is carried forward under the distributor 1.

Below the fiber layer forming surface 5 a suction box 6 is mounted. This suction box is connected to a suction pipe 7.

The distributor 1 comprises a planet stirring device, consisting of a vertical main shaft 8, which is supported by the top wall on the distributor by means of a bearing 9. To the main shaft 8 two horizontal supports 10 are fastened, at the ends of which bearings 11 are provided, which support two auxiliary shafts 12, each of which having at their bottom ends four impellers 13 which form a cross and the bottom edges of which move closely above the screen 4.

At their top ends the auxiliary shafts 12 are provided with friction wheels 14, which are in mesh with the inside of a cylinder surface 15 placed on the top wall of the distributor.

Directlyabove the screen 4 in the sidewall in the bottom part 3 of the distributor there is provided a short slit 16. At the slit 16 there is mounted a sliding plate 17 which is vertically adjustable by means of screws 18 so as to change the height of the slit l6.

At one end of the slit 16 there is mounted an air nozzle 19 which is connected with a pipe 20 for supplying air. The open end of the lump discharge pipe 21 is located close to the slit 16 at the exterior side of the distributor l.

The apparatus also comprises an inlet opening 22 for supplying a gas containing suspended fibers to the distributor l.

The operation of the apparatus is as follows:

Through the inlet opening 22 a disintegrated fibrous material is fed into the distributor l, suspended in a stream of air. At the same time there is maintained an air current through the fiber layer forming surface by means of the suction box 6. Consequently, the individual fibers which have a suitable direction and size, allowing them to pass down through the screen 4, will be deposited on the gas permeable forming surface 6.

The rotating impellers l3 partly distributes the fibers uniformly acrossthe screen and partly disintegrates loosely coherent fibrous wads. The fibrous lumps, which neither can pass the screen nor be disintegrated by the mixing device, will move along the screen due to their relatively high specific gravity. During the motion they pass the slit [6 at a certain time, whereby they are seized by the air current through the nozzle 19 and carried away through the slit 6 and into the discharge pipe 21, which may be connected with a defibrating device not shown. The defibrating device may comprise a pipe for recycling fibers to the distributor 1.

By regulating the height of the slit 16 by means of the sliding plate 17 a bigger or smaller part of the fibrous lumps on the screen 4 can be removed from the distributor.

I claim:

1. An apparatus for uniformly distributing a disintegrated fibrous material on a fiber layer forming surface, comprising a housing having a perforated plane-surfaced bottom wall, inlet means for a stream of gas containing suspended fibers and a stirring device having at least one impeller mounted for rotation a short distance above and in noncontacting relationship with the upper surface of said perforated bottom wall.

2. An apparatus as in claim 1, wherein the stirring device consists of a central shaft supporting at least two auxiliary shafts, each shaft having at its upper end means engaging with an annular ring connected to the top wall of said housing and having at its lower end an impeller mounted thereto.

3. An apparatus as in claim 1, wherein a narrow slit is provided in the sidewall of the housing adjacent said bottom wall and wherein an air same is mounted at the slit, said air nozzle being connected to a source of compressed air and being mounted so as to allow an air current produced in the same to pass out through the slit. 

2. An apparatus as in claim 1, wherein the stirring device consists of a central shaft supporting at least two auxiliary shafts, each shaft having at its upper end means engaging with an annular ring connected to the top wall of said housing and having at its lower end an impeller mounted thereto.
 3. An apparatus as in claim 1, wherein a narrow slit is provided in the sidewall of the housing adjacent said bottom wall and wherein an air same is mounted at the slit, said air nozzle being connected to a source of compressed air and being mounted so as to allow an air current produced in the same to pass out through the slit. 